[CVE-2026-90046][MODERATE 7.0] mm/page_alloc: don't spin_trylock() in NMI on UP [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-90046
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm/page_alloc: don't spin_trylock() in NMI on UP [ Upstream
Commit: 06c76d3c389ff504052f64b1acee44651bd847fa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=06c76d3c389ff504052f64b1acee44651bd847fa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90046
Analysis date: Wed, 16 Sep 2026 06:45:38 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-90046 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90046

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-90046	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90046 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-667;CWE-362;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'free_pages_nolock can reach __free_frozen_pages with FPI_TRYLOCK from NMI context on non-SMP builds and the old guard did not use can_spin_trylock for this case. Using spin_trylock in this context can be unsafe and may corrupt page allocator state or crash the kernel when a BPF tracing program exercises the path from NMI. For the CVSS the PR:L is used because the realistic attacker is a local user or local process able to run relevant BPF tracing code or equivalent delegated tracing capability, while deployments that restrict BPF to full administrators may treat this as PR:H operationally. The issue is not network reachable. Impact is at least local denial of service via kernel crash and the patch context explicitly notes probable local privilege escalation, so the paranoid impact uses C:H/I:H/A:H and requires manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)  SKIP CVE-2026-90046 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	BPF SIMPLEFIX LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +2: Class B active kernel state corruption candidate. The bug is unsafe `spin_trylock()` use from NMI context on UP/non-SMP in the `free_pages_nolock()` / `__free_frozen_pages()` page allocator free path. This is not a mere WARN-only issue because it can violate allocator locking assumptions.
* +1: Reliable kernel crash / strong DoS. The supplied commit text explicitly says this might crash the kernel.
* +1: Weak LPE concern. The commit text explicitly states it is probably exploitable by local attackers for privilege escalation, but no controlled reclaim, arbitrary write, or concrete exploit chain is supplied.
* +1: High-value core MM allocator path. The affected state is page allocator state, not isolated driver-local bookkeeping.

Paranoid signals:

* +2: Same Class B active kernel state corruption candidate.
* +1: Kernel crash / DoS.
* +2: Stronger but still grounded LPE concern. The affected primitive is in `mm/page_alloc.c`, involves allocator locking from NMI context, and the commit itself states probable local privilege escalation.
* +1: High-value core MM allocator path.

Important non-awarded signals:

* RealUAF not awarded. The patch does not establish a use-after-free or stale post-lifetime object use.
* Concrete repeated release/refcount not awarded. No double put, double free, or second lifetime mutation on the same dangling reference is shown.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity are not independently scored from a demonstrated primitive. They remain part of the unresolved LPE concern rather than separate positive signals.
* Remote reachability not awarded. This is a local/BPF/tracing/NMI path, not a network packet-processing trigger.
* Race/timing penalty not applied. The issue involves NMI context constraints, but the supplied evidence does not establish a narrow attacker-uncontrollable race window as the main requirement.
* Host-admin penalty not applied. BPF/tracing privilege requirements are unresolved from the supplied text, and host-admin-equivalent privilege is not positively established.
* Rare hardware penalty not applied. UP/non-SMP is a configuration constraint, but not physical-only or special hardware.

3. Reachability analysis

The likely trigger involves BPF programs using `free_pages_nolock()` related features in NMI context, probably tracing, on non-SMP builds. This is a local attack surface, not a direct remote one.

BPF privilege scope is not fully resolved from the supplied patch. Loading and attaching BPF tracing programs may require CAP_BPF, CAP_PERFMON, CAP_SYS_ADMIN, or other product-specific policy depending on kernel configuration and distribution defaults. Therefore `HostAdminRequired=UNKNOWN`, not YES or NO.

The complete trigger chain is not proven namespace-scoped. No supplied evidence shows that an attacker can create a namespace, obtain the needed capability there, load or attach the relevant BPF program, and trigger the NMI path completely below host admin. Therefore `NamespaceScopedPrivilege=UNKNOWN`.

Prior privileged setup may exist in real deployments if BPF tracing is restricted or disabled, but the prompt evidence also says local attackers may exploit it. This uncertainty suppresses ordinary-unprivileged scoring but does not justify a host-admin downgrade.

Special prerequisites are present: non-SMP/UP build and BPF/tracing use in NMI context. These reduce broad exposure in practice, but they do not remove the need for manual review because the affected primitive is in core page allocator state and the commit explicitly flags probable privilege escalation.

4. Primitive and severity interpretation

The exact primitive is unsafe locking in the page allocator free path: `__free_frozen_pages()` used a narrower condition that avoided the unsafe trylock case only for `CONFIG_PREEMPT_RT` with NMI or hardirq, but missed other contexts where `can_spin_trylock()` would reject trylock use, notably NMI on UP/non-SMP.

This is not a UAF and not a concrete double-release bug. It is best classified as `CLASS_B`: a real kernel state corruption / allocator consistency primitive with unresolved exploitation leverage.

The demonstrated consequence is local kernel crash / DoS. The speculative but explicitly patch-supported consequence is local privilege escalation through allocator state corruption. Because the affected code is in the core page allocator and the commit author explicitly calls out probable local exploitability, this should not be treated as an ordinary low-priority crash-only bug.

`ImportantCandidate=YES` because the primitive is in core MM allocator state and the LPE concern is explicitly stated but not fully resolved. `AutoDowngradeAllowed=NO` because automatic closure would discard a meaningful unresolved kernel corruption and LPE question.

Likely operational severity: actionable Moderate at minimum, with Strong Important candidacy requiring human review, especially for products where relevant BPF/tracing features are available below full host-admin privilege.

5. One-sentence report phrase

Unsafe `spin_trylock()` use from NMI context on UP/non-SMP in the `free_pages_nolock()` page allocator free path can crash the kernel and is explicitly described as probably exploitable by local attackers for privilege escalation, but the complete BPF privilege boundary and exploit primitive require manual review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: core page allocator state is affected, the patch context explicitly mentions probable local privilege escalation, and BPF/tracing privilege reachability is product-dependent.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: mm/page_alloc: don't spin_trylock() in NMI on UP [ Upstream
Commit: 06c76d3c389ff504052f64b1acee44651bd847fa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=06c76d3c389ff504052f64b1acee44651bd847fa

Changed files:
  mm/page_alloc.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=06c76d3c389ff504052f64b1acee44651bd847fa

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-90046 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90046

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 5
  Paranoid ActionableScore: 6

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).